1. Field of the Invention
The present invention relates to a composition for gluing discontinuous mineral fibers, in particular glass fibers. It also relates to insulation products, treated using said composition, which in particular have a white color and which are particularly useful in the form of shells for pipe insulation or cushions for the manufacture of molded products.
2. Background of the Prior Art
Mineral fiber-based insulation products can be formed from fibers obtained by various methods. For example, the technique known as centrifugal drawing can be mentioned, in which the molten material is placed into a centrifuge containing a multitude of small orifices, projected under the action of the centrifugal force towards the peripheral wall of the centrifuge and is released therefrom through the orifices in the form of filaments. On exiting the centrifuge, these are drawn and driven towards a receiver component by a high speed and high temperature gas current. To ensure the assembly of the fibers with one another in order to obtain an insulation cushion, the fibers are treated with a so-called, glue composition which contains a heat-hardenable resin. The cushion of treated fibers is then subjected to heat treatment in a drying chamber so as to polymerize the resin and obtain an insulation product having the desired properties, such as resilience, stability in size, traction resistance, thickness recovery after compression and homogeneous color.
The glue compositions generally contain a heat-hardenable resin. However, glue compositions containing only a heat-hardenable resin would form products with a non-homogeneous color, which are more expensive and would make the method of manufacture more polluting. Therefore, the glue compositions normally used contain an aqueous resin composition acting as the principal binder and glue additives which give the final product suitable properties and satisfy the requirements inherent to the method of manufacture of the product. The resin is generally comprised of phenoplast resins (phenol-formol) or aminoplast resins (melamine-formol).
The treatment of the fibers using the glue composition can be carried out in different ways. For example, the fibers can first be assembled on the receiving component, such as a conveyer, they can be compressed into a cushion and then dipped in an aqueous solution containing phenoplast or aminoplast resins, or mixtures thereof. However, it is necessary to remove the water. The subsequent heat treatment therefore serves to remove the water and to polymerize the resins, which leads to further high energy use.
Therefore, the fibers are preferably treated on exiting the drawing component by spraying them with an aqueous glue composition. The water is then partially evaporated and the subsequent heat treatment is used essentially for the final drying, the polymerization of the resins and the shaping of the cushion of bound fibers.
For such a treatment using spraying, it is necessary to use a glue composition which can be easily sprayed on the fibers. For this purpose, the essential ingredient of the glue composition, i.e., the heat-hardenable resin, must, in addition to good stability over time, have a high rate of dilutability (or water tolerance) in water. This high rate of dilutability also provides the resin with an appropriate gelling time in order to prevent polymerization which is too rapid, enables homogeneous distribution on the fibers and, consequently, provides more uniform gluing of the fibers. The rate of dilutability in water of an aqueous resin solution corresponds to the volume of deionized water which, at a given temperature, can be added to the volume unit of said solution before causing the formation of a permanent cloud.
To obtain glue compositions which are easily sprayable on the mineral fibers, it was thought to use melamine-urea-formaldehyde type resins, which result from a condensation reaction in a basic medium of formaldehyde, urea and then melamine, in the presence of a polyol having a functionality of at least equal to three. These resins are stable over time and can have a dilutability (or water tolerance) at least equal to 1000%. The glue compositions containing these resins are easily sprayable on the mineral fibers, have an appropriate gelling time and enable insulation products to be formed which hold well in heat and have a white color.
While these glue compositions provide insulation products having improved properties, they still have certain disadvantages. First of all, they contain a particular resin (melamine-urea-formaldehyde prepared in the presence of a polyol), the manufacture of which is more expensive than that of other resins of the same type. On the other hand, the fibers, after drawing and treatment with the glue composition, are collected on a receiving component where they form a cushion which can have a sticky character, which prevents sufficient reinflation of the cushion before the heat treatment for the polymerization of the resin. This insufficient reinflation prior to polymerization (pregelling) does not provide a product having good thickness recovery after the compression necessary for the economical stocking and transportation of the products. In addition, it is sought to obtain products having improved mechanical properties, in particular traction resistance.